Introduce KZGProof as its own type instead of using KZGCommitment

EIPS/eip-4844.md

@@ -73,6 +73,7 @@ Compared to full data sharding, this EIP has a reduced cap on the number of thes
 | `Blob` | `Vector[BLSFieldElement, FIELD_ELEMENTS_PER_BLOB]` | |
 | `VersionedHash` | `Bytes32` | |
 | `KZGCommitment` | `Bytes48` | Same as BLS standard "is valid pubkey" check but also allows `0x00..00` for point-at-infinity |
+| `KZGProof` | Bytes48 | Same as for `KZGCommitment` |
 
 ### Helpers
 
@@ -103,7 +104,7 @@ Verifies a KZG evaluation proof:
 def verify_kzg_proof(polynomial_kzg: KZGCommitment,
                      x: BLSFieldElement,
                      y: BLSFieldElement,
-                     quotient_kzg: KZGCommitment):
+                     quotient_kzg: KZGProof):
     # Verify: P - y = Q * (X - x)
     X_minus_x = bls.add(KZG_SETUP_G2[1], bls.multiply(bls.G2, BLS_MODULUS - x))
     P_minus_y = bls.add(polynomial_kzg, bls.multiply(bls.G1, BLS_MODULUS - y))